Earth-boring tools for forming wellbores in subterranean earth formations may include a plurality of cutting elements secured to a body. For example, fixed-cutter earth-boring rotary drill bits (also referred to as “drag bits”) include a plurality of cutting elements that are fixedly attached to a bit body of the drill bit. Similarly, roller cone earth-boring rotary drill bits may include cones that are mounted on bearing pins extending from legs of a bit body such that each cone is capable of rotating about the bearing pin on which it is mounted. A plurality of cutting elements may be mounted to each cone of the drill bit.
The cutting elements used in such earth-boring tools often include polycrystalline diamond compact (often referred to as “PDC”) cutting elements, also termed “cutters,” which are cutting elements that include a polycrystalline diamond (PCD) material, which may be characterized as a superabrasive or superhard material. Such polycrystalline diamond materials are formed by sintering and bonding together relatively small synthetic, natural, or a combination of synthetic and natural diamond grains or crystals, termed “grit,” under conditions of high temperature and high pressure in the presence of a catalyst, such as, for example, cobalt, iron, nickel, or alloys and mixtures thereof, to form a layer of polycrystalline diamond material, also called a diamond table. These processes are often referred to as high temperature/high pressure (“HTHP”) processes. The cutting element substrate may comprise a cermet material, i.e., a ceramic-metal composite material, such as, for example, cobalt-cemented tungsten carbide. In some instances, the polycrystalline diamond table may be formed on the cutting element, for example, during the HTHP sintering process. In such instances, cobalt or other catalyst material in the cutting element substrate may be swept into the diamond grains or crystals during sintering and serve as a catalyst material for forming a diamond table from the diamond grains or crystals. Powdered catalyst material may also be mixed with the diamond grains or crystals prior to sintering the grains or crystals together in an HTHP process. In other methods, however, the diamond table may be formed separately from the cutting element substrate and subsequently attached thereto.
As the diamond table of the cutting elements interacts with the underlying earth formation, for example, by shearing or crushing, the diamond table may delaminate or fracture because of the high stresses placed thereon. Some cutting elements may include recesses, such as, for example, grooves, depressions, indentations, and notches, formed in the cutting element substrate. The diamond table may include correspondingly mating protrusions. Other cutting elements may locate the recesses in the diamond table and the mating protrusions on the substrate. The increased contact area at the interface between the substrate and the diamond table may prevent delamination by strengthening the bond between the diamond table and the substrate. Conventionally, the recesses and correspondingly mating protrusions are symmetrical about at least one axis. An exemplary, conventional type of interface design is depicted in FIGS. 1 and 2. As shown in FIGS. 1 and 2, a cutting element substrate 10 includes a symmetric interface feature 12. The symmetric interface feature 12 is a recess or depression formed in an end of the substrate 10. The interface feature 12 comprises a plurality of radially extending grooves that terminate or truncate before reaching the peripheral edge of the substrate 10. In other words, the symmetric interface feature 12 may be said to resemble the spokes of a wheel, or an asterisk. Planes 14-14 through 24-24 (shown in the two-dimensional view of FIG. 1 as lines or axes) represent six planes intersecting a central axis 26 of the substrate 10, the intersection comprising the central axis 26, not merely a single point thereof, about which the symmetric interface feature 12 is symmetrical. In addition, the symmetric interface feature 12 shown in FIG. 1 is symmetrical about a plane (not shown) parallel with a top end surface of the substrate 10 that lies halfway down the depth of symmetric interface feature 12.
Elastic waves generated from impact and other high-stress short duration events during stable or unstable earth drilling can contribute to diamond table fracture, delamination, and even catastrophic failure of the cutting element, eventually resulting in failure of the drill bit. The elastic stress waves are usually generated at the point of contact between the cutting face of the diamond table and the underlying earth formation, but they may also be generated elsewhere within the cutting element, bit blades, drill bit, or drill string and propagate through the cutting element. Surfaces and interfaces between dissimilar materials, such as, for example, a cutting element and open air, liquid, or rock; the interface between a diamond table and a cemented tungsten carbide substrate; or the interface between a cemented tungsten carbide substrate and a braze material in pockets formed in blades of the a drag bit are just some examples where elastic stress waves can reflect, concentrate, and even cause failure. In addition to material properties, the geometry of the material or materials through which the waves propagate may contribute to stress wave amplification at these interfaces or at the surfaces defining the solid structure, such as the cutting face or periphery of the diamond table.